Capture of gases emitted from power plants is an area of increasing interest. Power plants based on the combustion of petroleum products generate carbon dioxide as a by-product of the reaction. Historically this carbon dioxide has been released into the atmosphere after combustion. However, it is becoming increasingly desirable to identify ways to find alternative uses for the carbon dioxide generated during combustion.
Combined cycle power plants provide an efficient way to generate electricity from the burning of petroleum products or other carbon-based fuels. Combined cycle power plants can leverage an initial combustion reaction to power multiple turbines for generation of electricity, leading to more efficient power generation. However, conventional methods for capturing carbon dioxide tend to reduce the efficiency of electricity generation, due to the additional energy required to capture and/or sequester the carbon dioxide.
PCT International Publication No. WO/2012/003079 describes systems and methods for generating electricity using a combined cycle power plant based on combustion of carbon-based fuels. The systems and methods include use of stoichiometric ratios of fuels to oxygen in the combustion reaction as well as recycling of combustion exhaust gas as part of the input to the combustion reaction. The combustion products are withdrawn from the system as a purge gas stream. The CO2 in the purge gas stream is removed, for example, using a solvent such as potassium carbonate.
U.S. Pat. No. 6,902,602 describes methods for performing separations by swing adsorption where it is desirable to minimize or avoid interaction between one of the components in a gas stream being separated and a component of the gas stream used for purging the swing adsorption apparatus. Separations of hydrogen and carbon dioxide from syngas stream are noted as an example, where it is desirable to avoid contamination of the hydrogen product stream with any oxygen from the typical oxygen-containing purge stream. The separation methods include use of one or more buffer gas steps during a separation, where a buffer different from any other components is used to prevent contamination between steps of a separation process.
U.S. Published Patent Application No. 2012/0125194 describes an autothermal cycle for CO2 capture. A combustion exhaust gas is contacted with an adsorbent bed to adsorb CO2. The CO2 is then removed by contacting the adsorbent with a gas comprising steam. The resulting output gas containing steam and CO2 is conveyed to a vapor recompression system to recover H2O, CO2, and heat. The recovered H2O and heat are then used to provide steam for the sweep gas. The amount of steam sweep gas required for recovery of CO2 is described as being ˜1 mole of steam per mole of input feed gas. The flue gas input feeds are described as having a CO2 content of 15 mol % or less. Thus, the steam/CO2 molar ratio is described as being at least ˜6 moles of steam per mole of CO2. The process is described as recovering at least 90% of the carbon in the combustion exhaust gas as part of the output gas.
U.S. Published Patent Application No. 2013/033391 A1 describes a system reducing or mitigating emissions during power generation. The system uses the recycled exhaust gas from a power generation combustion reaction and separates it using a swing adsorption process so as to generate a high purity CO2 stream. This in turn reduces the energy required for the separation, without having to reduce the temperature of the exhaust gas. However, the processes described in this application have several drawbacks. The pressure swing adsorption process requires removing CO2 from the adsorbent bed using a steam purge, however, this process takes away steam which would otherwise be used as energy in the main combustion cycle. Additionally the removed CO2 in this cycle has a pressure of only 1.0 to 3.0 bar. CO2 kept at such a low pressure takes up a lot more volume than CO2 kept at a higher pressure, and thus this system has a high footprint as it requires more piping and the like to store and move the low pressure CO2. Further, the cryogenically storing of CO2 typically requires bringing the pressure of the CO2 to 100 bar. Thus it is more energy intensive to cryogenically store the CO2 of this system than it would be if the pressure outputted was higher. Also, the steam purge used in this system places corrosive stress on the piping used to carry out the PSA process.
Other potentially relevant publications can include U.S. Patent Application Publication No. 20120318533, European Patent Application No. EP 2220338, an article by Reijers et al., Ind. Eng. Chem. Res., 2009, 48, 6966, and an article by Wright et al., Energy Procedia, 2011, 4, 1457, inter alia.